the manifold block. This particular manifold consists mostly
of 6 mm I/O ports. The smaller pair of A/B ports measures
in with an outside diameter of 4 mm. The P and R
commons mate with 8 mm polyurethane or nylon tubing.

The SMC engineers have done their thing and given
us a pretty good set of pneumatic switches. All we have to
do to put the manifold valves to work is lash up some
microcontroller doorbell circuitry.

Air Traffic Control via a
PIC Microcontroller

I have three microcontroller doorbell solenoid driver
circuits to offer you. I call them doorbell circuits because all
we really have to do to drive the valve’s pilot solenoids is
switch 24 VDC to their coils with a transistor or MOSFET.
A microcontroller doorbell circuit is simply the pilot
solenoid driver circuit with a microcontroller I/O pin
in control of the switch.

The first pilot solenoid driver circuit is the simplest
and cheapest to implement. The NUD3160 integrated
relay, inductive load driver is a comprehensive solenoid
coil driver that is designed for automotive use. The
NUD3160 can switch inductive loads up to 60 VDC @
150 mA. As you can see in Schematic 1A, all of the
BEMF protection is built into the NUD3160. So, there’s
no need for the external free-wheeling diode that is

normally placed across the solenoid coil. The disadvantage
to this solution is that the solenoid load is not fully isolated
from the PIC’s I/O pin. The PIC and the solenoid share a
common ground and a catastrophic failure of the NUD3160
could damage the PIC. The NUD3160 is very sturdy and you
would really have to put forth a concentrated effort to
release its magic smoke.

The circuit shown in Schematic 1B uses an HSR312
photovoltaic solid-state relay optocoupler to isolate the PIC
from the valve’s pilot solenoid coil. The PIC’s I/O pin only
sees the HSR312’s LED and its 8 mA load. The HSR312’s
internal MOSFETs — which are under the internal LED’s
control — do the heavy lifting. The parallel connection of
the MOSFETs provides a current handling capacity of

Coast Pneumatics

www.Coastpneumatics.com

AutomationDirect

www.automationdirect.com

S
O
U
R
C
E
S

SMC Manifolds
SMC SY3000 Manifold Parts

www.coastpneumatics.com

Polyurethane Tubing
www.automationdirect.com

PIC Microcontrollers
Microchip
www.microchip.com

PLC Center
www.plccenter.com

eBay
www.ebay.com

NUD3105
HSR312
Mouser
www.mouser.com

NUD3160

ON Semiconductor

www.onsemi.com

A

B

C

24VDC

24VDC

24VDC

5VDC

5VDC

5VDC

470

SOLENOID COIL

470 SOLENOID COIL

470 SOLENOID COIL

1N4007

1N4007

DRAIN 3

1 ANODE

6 DRAIN

1 ANODE

6 DRAIN

OPTIONAL
VISIBLE LED

NUD3160

1 GATE

TO PIC I/O PIN

5 SOURCE

SOURCE 5

HSR312

HSR312

2 SOURCE

2 CATHODE

4 DRAIN

2 CATHODE

4 DRAIN

TO PIC I/O PIN

COMMON GND

24VDC GND

3 DRAIN

DRAIN

NUD3105

5VDC GND

1 GATE

24VDC GND
TO PIC I/O PIN

5VDC GND

2 SOURCE

SCHEMATIC 1. If isolation is not important, and cheap, quick, and easy are your goals, build circuit A.

For safety and isolation, you’ll want to use circuit B. To optimize the PIC’s I/O capabilities, add the buffer in circuit C.